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I acquired this telescope during the summer and as the season hasn't yet begun I've only had a few short test sessions so far. I don't have access to my test images as I write this, but I was a bit concerned with the sharpness compared to my old Evostar 80ED. I ran a few subs through ASTAP to check for any anomalies and found out that there was about 13-14% tilt. The scope was bought from FLO so supposedly it's been checked and tuned before shipping as they state on their website, but how much tilt is generally acceptable? I've not had a chance to do further tests but I have made some changes to my setup in order to do so. Initially this was my image train: Scope > SW Flattener > ZWO OAG > 11mm spacer > 1mm male to male M48 thread > ZWO 8x1.25" EFW > Shim > ASI533 Total backfocus is just above 55mm, the shim is there in order to adjust for my filters. For my next test I've removed my OAG and replaced it with the 16.5mm spacer in stead as I figured this could be a potential culprit. Another culprit might be the flattener. With my other/previous scopes I haven't had any issues with tilt so I've not had to deal with this before. |
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At least for my Esprit80ED the Backfocus of the Flattener was more 56.5 mm instead of the official 55mm, you should use Nina‘s aberration inspector to dial in Backfocus. The old ZWO OAG can be tricky with tilt, the new, bigger version with the extra tilt plate is more stable. So removing the OAG was a good first step. Did you check if there is any up/down movement of the camera when you are at focus point? It should not be but it is an easy test so worth doing as 14% tilt is huge… Also, usually the OAG should be close to the filter wheel, otherwise you will have a hard time to dial in Backfocus for your guiding camera, it has to stick out those extra 11mm of the spacer. The new OAG can be screwed to the filter wheel which is the best solution anyway, but unfortunately not possible with the old OAG. Michael |
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| I have seen examples of ZWO OAGs causing tilt, where the ring that sits inside the main body of the OAG doesn’t sit flush (more obvious if you rotate it around a little - see if it rises/falls with movement). Also I have seen examples of some slop in the Esprit focuser. This isn’t the case with mine but I’ve seen others that can wobble a little when a small amount of pressure is applied (given that focus is generally right out at the extremity of the focusers range). I did have tilt for a while but this was solved once I had the OAG-L bolted to 2” EFW which was then bolted to the ASI2600 (so my issue was certainly with the image train). This may not help but this is what I’ve seen to date :-) |
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4.36
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Michael Ring: Good info, I'll have a look at some of my subs just to see if there should be more spacers added. It is the old version, or v2 to be precise - but it is a bit of a weak point considering how it attaches to the camera side of the image train. Not very reliable. I didn't check that purposefully, but I can't say I noticed any movement at all, besides the fact that the three screws holding the camera in the OAG could easily misalign the whole setup. 14% had me a bit worried, especially as it's a fairly expensive scope by my accounts. But I want to make sure I've done what I can before I contact the vendor. Yes, the issue I had though was that the OAG easily collided with the EFW but I managed to get focus by removing the spacer on my 174mini as it had to get really close. Thanks for the reply! |
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Ben: Thanks! It makes me feel a bit more at ease since the issue might very well be the OAG as I suspected. I noticed the exact thing you mention here, and it's tricky to get it 100% right. Even though I have a smaller camera it is a bit of weight sitting at the mercy of three mediocre screws. I'll have a look to see if the tube has any movement. I haven't noticed anything so I don't think that's an issue. I did however notice when disassembling that the rear piece of the flattener came loose a tiny bit when I unscrewed the spacers, I tightened it back up right away - but I'm not sure if this is the bit holding the glass. |
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 Here's the master stack with the aberration inspector tool in PI   I tried looking at the single subs as well and the tilt varied quite a bit, so I'm guessing it makes more sense to look at the master? |
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Here's the second stack, the camera was slightly rotated between taking these frames, otherwise the same image train with OAG.   |
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4.36
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Got the opportunity to do further testing last night after replacing the OAG with a 16.5mm spacer and tightening the rotator on the tube all the way back to zero. I also had to adjust the EAF setup as it was a bit sloppy so I had to remove the bracket and screw it back on afterwards. The results from last night were even worse though. I shot a few 30s frames luminance and Oiii which had about 15-20% tilt. I also checked several 300s Oiii and Ha subs from during the night but they yielded 25-30% tilt. I'm not quite sure what's going on here, the only thing I haven't done is removing the flattener in order to test the field without it, maybe that should be my next step for tonight. One other notice: When I was adjusting my image train I noticed that the rear piece of the flattener with the threads (not sure what to call it), came off slightly when removing the spacers/OAG. My thoughts so far: 1. The flattener might be an issue, especially as the results got a lot worse after adjusting the image train, also considering the threads got unscrewed a bit in the process. 2. It's the scope, although checked and tuned by the supplier, I have fitted the EAF bracket using the outer screws on the focuser (not the inner ones). Could this have done something to the tube? 3. Might be a combination all things considered. |
9.48
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It took me two full years to minimize the tilt with my Esprit 100ED such that I was satisfied with it. The first thing I can say is that the large black rings that supposedly allow you to rotate the camera should be tightened and left that way. The rear back ring should be screwed in all the way clockwise until it's completely tight, and then the front ring should be clamped down on it hard. Sorry, but it's not going to allow you to rotate the camera unless you want to fight with tilt forever. I'm not the only person who came to this conclusion. The second piece of advice is to consider getting a Gerd Neuman 48 mm CTU if your imaging train has enough room. I use a guide scope, not OAG, so I could afford to insert the CTU. Glad I did, because it was the first time I ever had good stars in all four corners. The last piece of advice is not to get too dependent on analysis software. What you're really looking for is stars that are 1) round 2) in focus, in all four corners. I have used software to analyze the tilt, and when it said the tilt was gone, I still had obviously bad stars in one corner. I then adjusted the CTU back to where I started and use the "eye test" in aberration inspector to look at corner stars. If you can't see anything that bothers your eye, it's good enough, so just have at it. Who cares what the software says if the corner stars look good? So many otherwise fine images on Astrobin have obvious star distortions in the corners, so if your images don't, I feel like you're above the bar. Finally, be prepared for slight changes in back-focus and tilt as the temperature changes outside. In going from summer to winter in my climate, I will need to make adjustments sooner or later, or just accept that the back-focus has changed a little over the preceding months. Also, my Esprit 100ED has pinched optics and suffers from star distortions in cold weather, so there's nothing I can do about ugly stars in January - but it's still my favorite imaging telescope. |
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It took me two full years to minimize the tilt with my Esprit 100ED such that I was satisfied with it. Thanks for the reply, it's very much appreciated to be hearing back from other users! I have been doing more tests and did exactly what you are describing here with the rotator. I did 90 degree rotations from 0 to 270 degrees to see if there were any changes, ASTAP says there is some tilt - but I've been trusting it less and less due to the varying results it yields. The stars look good now, I have a small sensor (533MM) for now but it's going to have a 2600 on there sooner or later. The vendor also says that the stars look good, but also stated that some of my test image sets has focus issues - which I found a bit strange as I was using the EAF and the AA+ autofocus routine for each frame/rotation. The tightening of the rotator might have made the biggest difference as it was originally a bit too far out. What I did notice though is that the HFD or star size became smaller as I rotated the camera towards 270 degrees, being at it's smallest around 180-270. This could be a simple case of other factors in the atmosphere but still. After the adjustments I haven't been doing any NB work, so I haven't seen if the sharpness has improved for the nebula, but it was obviously something wrong with the first images I took with the scope. This is from one of the first image sets, 300s Ha. The stars look terrible to me. And the nebulosity was far sharper on my Evostar 80ED.  This is from my red filter after tightening the rotator and rotating it 270 degrees before locking it down, 270 gave me the best values in ASTAP at the time, that's why I chose it. I'm not seeing the same kind of coma here.  I guess some kind of focus issue could be the answer to the issues that had me reacting in the first place. But I'm not quite sure what to change as there is no slip in the tube. I'm just hoping that it is performing better on sharpness on nebula from here on out. |
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I'm not sure how you rotated your camera, but rotating the black rings actually changes the back-focus measurably. The threads are very crude, so one rotation of the back rings will make a noticeable difference in the corner stars. It's possible that when you reached 270 degrees, you had the back-focus exactly right, so the properly focused stars were smaller. I have definitely seen this effect myself while playing with the black rings some time ago. You could try tightening the rings completely and adding a few < 1 mm plastic spacers to increase the back-focus bit by bit until you get the smallest possible stars. It's tedious, but it's worth it to have those rings tight so there is no possibility of flexure where the two rings come together. Otherwise, the tilt can (will) change as the elevation of the target changes, which is going to provide hours and hours of frustration and confusion. I had a lot of trouble with my 100ED when I got it in 2020. You'll find some older posts here where I was unhappy with it for various reasons. My first images with it were terrible compared to what I was getting with my C11 EdgeHD, and I could not get rid of the tilt. In addition to an enormous amount of tinkering, I bought a lot of new accessories: hardware to make the guide scope rig as rigid as possible, a PegasusAstro FocusCube, switched to NINA autofocus from manual focusing (which is a complete no-go), new guide camera, new main camera (QHY268M), Gerd Neumann CTU, new filter wheel, and finally, a set of Chroma filters. Whew - all of that cost more than the telescope. At this point, the only problem I have is the pinched optics in cold weather. The new filter set and new camera were equally important, to my surprise. Switching from my old CCD camera to a new CMOS camera (QHY268M) with lower noise provided a much larger field of view and a serious increase in image quality, which I expected. However, I didn't realize how important the filters were. When I switched to Chroma filters last fall, I could not believe the difference compared to my set of less expensive (name brand omitted) LHRGB filters with the same camera. The less expensive set actually set me back $450 plus $180 for the H-alpha, so they weren't that cheap. I wish I had that money back, along with the time I spent on them. The Chroma filters wiped out any trace of bloated stars or halos, and white stars are actually white now. I barely have to do any tweaking to the stars during processing. Chromatic aberration is not an issue at all. I seldom advocate strongly for any particular gear, but I can attest to these filters making a large difference in the performance of the Esprit/QHY268M rig. (I have also heard good things about Astronomik filters, but I can't use them with my rig due to a mechanical spacing issue that probably doesn't affect anyone else.) I see you are using 1.25" Antlia filters, but if you intend to get a new set at some point, get 36 mm filters and a compatible filter wheel. 36 mm will cover an APS-C sensor with no problem. I don't think I would want to try dealing with the tilt problem with a full-frame sensor and this telescope, so I'm stopping with APS-C. |
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I hadn't thought of that, I have about 56mm backfocus from the sensor to my flattener but I didn't even consider that the black rings would affect this in any way. Even though I had to refocus for every rotation. I guess I'm tightening the whole thing back up now, feel like I opened up a whole can of worms with this telescope so far. You are probably right though, as the stars look a lot better while rotated, would adding some shims between the flattener and sensor help? I originally thought that the backfocus distance between those two was "set", as in anything in front of the flattener shouldn't affect this number. I suppose the best way forward is to tighten therings and use a bahtinov to double check, then adding some shims. Thanks for the help so far, finally feels like I'm getting somewhere  Edit: So far I am very pleased with the Antlia filters, though I haven't had them for more than half a season combined and haven't gotten that much mileage on them. I was thinking of getting the same filters for the 2600 I am considering, just in 2" size. I'm sure Chroma has the upper hand, but boy do they cost.. |
